Separating system



June 11, 1963 G. L. WlLMOT SEPARATING SYSTEM 2 Sheets-Sheet 1 FiledSept. 30, 1960 INVENTOR.

G06 L w/L M07 BY jig MA.

June 11, 1963 s. L. WILMOT 3,093,577

SEPARATING SYSTEM Filed Sept. 30. 1960 2 Sheets-Sheet 2 .97 I L I 52/0AMPL/F/EE name I 9y 1 #7 9.2 93 9a 9: 96 I J L IN VEN TOR. GEO/96A 1.Kill. M07

A rive/v5 X United States Patent Ofice 3,093,577 Patented June 11, 19633,093,577 SEPARATING SYSTEM George L. Wilmot, Pocono Lake, Pa., assiguorto Wilxnot Engineering Company, White Haven, Pa., a corporatlon ofPennsylvania Filed Sept. 30, 1960, Ser. No. 59,736 21 Claims. (Cl.209-1725) This invention relates to improvements in a system forseparating coal or the like from its raw material, and more particularlyconcerns a flotation separating process and system, and the automaticcontrolling of the density of the separating medium used therein.

Coal is graded as standard or substandard according to the amount ofinherent ash and waste materials (clay, rock, sand, slate and otherimpurities) it contains. To remove the impurities from raw coal andobtain clean coal of high quality, many breaker plants have adopted aheavy medium separating system which is also widely used in oreseparation. This float-and-sink method of removal of impurities uses aslurry of finely divided solids (for example, magnetite or ferrosilicon)in water. The specific gravity of the slurry medium is high enough toseparate the coal from the heavier waste materials, causing the coal tofloat off free of the heavier state, rock and other sink products.

However, there is a serious problem in the use of the float-and-sink"method of separating in that the density of the separating medium iscritical. Any variation in its density either causes extensive loss ofcoal, or causes the processed coal to have a high ash content, therebymaking it substandard.

As an example, if the optimum specific gravity of the separating mediumfor the coal being processed is 1.70, and the specific gravity drops,the system loses good coal which sinks in the separating medium with theheavy refuse and passes out to waste.

On the other hand, if the specific gravity of the separating medium istoo high, more near gravity refuse is floated with the coal than desiredso that the resulting coal product has an ash content which is too high.Accordingly, the coal product is not of good quality and either has tobe returned to the breaker for recleaning, or has to be sold assubstandard coal at a reduced price.

Keeping the density of the separating medium constant is a problem sincethe raw coal must be washed before being fed to the separating system,and it retains a good deal of the wash water. This water on the raw coalcontinuously dilutes the separating medium and lowers its density.

In addition to this dilution by the water from the raw coal, the mediumis constantly being diluted through the loss of some of its finelydivided solids which pass out of the system with the processed coal orwith the refuse. Provision is made to recover as much of the finelydivided solids as possible, but a small amount does continually escapefrom the separating system.

It has heretofore been proposed to attempt to control the density of theseparating medium by having a skilled operator test the density manuallywith a Denver cup. In this method, the operator scoops the slurry mediuminto a cup of a known size and then measures the specific gravity of themedium contained therein. If the specific gravity is too low, theoperator adds magnetite, and if the specific gravity is too high, theoperator adds water to the medium.

However, this Denver cup method has a number of disadvantages in thatthe specific gravity measurements are not too accurate, the measurementsare not made continuously, and no provision is made for adding the rightamount of magnetite or water, since the operator just adds the amount ofmaterial or water that he guesses will bring the density back to itsoptimum value.

Accordingly, it is an object of this invention to provide a separatorsystem which gives a high quality coal, with a minimum of coal goingwith the refuse to waste.

It is another object to recover a high percentage of the magnetite (orother finely divided solid) used in the separating medium, with verylittle of the magnetite passing out of the system with the coal or withthe refuse.

It is another object to provide a separator system wherein the densityof the separating medium is automatically and continuously controlledwith a high degree of accuracy.

It is another object to provide a separator system wherein the level ofthe mixing sump (of the separating medium) is maintained within apredetermined range.

It is another object to provide a separating system with means forcompensating for the water brought into the system with the raw coal tobe processed, and with means for shutting off said compensating meanswhen the raw coal is not being fed to the system.

Other objects and advantages of this invention including its simplicityand economy, as well as the ease with which it may be adapted toexisting equipment, will further become apparent herein and in thedrawings, in which:

FIG. 1 is a schematic view of a separating sysem constructed inaccordance with this invention, with electrical conductors leading to acontrol panel shown in FIG. 2;

FIG. 2 is a schematic view of the control panel forming a part of thisinvention; and

FIG. 3 is a schematic view illustrating the electric proportionalcontroller forming an element of the separating system.

Although specific terms are used in the following description forclarity, these terms are intended to refer only to the structure shownin the drawings and are not intended to define or limit the scope of theinvention.

Turning now to the specific embodiment of the invention selected forillustration in the drawings, there is shown a system for separatingcoal from raw coal containing coal and refuse, comprising a mixing sump11 into which is fed water and finely divided magnetite to form a coalseparating slurry medium, a coal-separating vessel 12 which receives theseparating medium through a conduit 13 extending from sump 11, meansincluding raw coal feed-conveyor 14 and prewet vibrator 15 for feedingraw coal into vessel 12, coal-separating means including coal-separatingvessel 12 and the separating medium contained therein for separating thecoal from the waste 'by causing the coal to float in the medium, meansincluding partitioned vibrator dewatering screen 16 for separating thecoal from the separating medium and returning the medium to sump 11, anddensit sensing and control means including density measuring head 17 andthe control panel of FIG. 2 for continuously measuring the density ofthe separating medium and automatically controlling the density byadding and subtracting water and magnetite to and from the system, inresponse to said measuring.

In operation, raw coal is delivered from the mine to the yard forwashing, separating, and sizing. The raw coal is passed over areciprocating picking table (where large rocks and timber are thrownout), and is crushed to size. Then it is delivered to perforatedpresizing and prewet vibrator 15, where coal smaller than one-quarterinch goes through conduit 18 directly to the fine coal cleaning systemfor sizing and shipment, and coal of larger size is delivered tocoal-separating vessel 12 for separating from ash. Prewet vibrator 15eliminates some of the Water on the raw coal to thereby reduce theamount of dilution of the separating medium caused by such Water whenthe raw coal enters coal-separating vessel 12.

The raw coal enters vessel 12 at the surface level of the separatingmedium contained therein, and travels along that surface to bedischarged as overflow through float conduit 21.

The rock and other refuse sinks to the bottom of vessel 12 where it isremoved by an oscillating rake and passes out through sink conduit 22.

Both the coal and the refuse pass separately to partitioned vibratordewatering screen 16 where the separating medium is recovered by the useof vibration and a series of sprays. Screen 16 is partitioned lengthwiseto allow the coal and the refuse to pass therealong separately anddischarge into separate chutes. The cleaned coal is elevated to sizingshakers and then transferred to retail coal pockets, and the refuse isdumped into bins for disposal.

The separating medium is recovered in the three sumps located beneathscreen 16: Main medium sump l1, washings sump 23, and rinsing sump 24. Afraction of the medium is recovered by draining it through the vibratingscreen deck 37 into the sump 11.

Another fraction of the medium is recovered in washings sump 23. Thismedium fraction has been diluted by Water from sprays 26, so it istransferred by pump 27 through conduit 28 to a magnetic separator 31where Water and fine coal particles are removed and the magnetite isrecovered. The fine coal is transferred to a fine coal sizing shaker(not shown) through conduit 32, and the water is disposed of throughconduit 33. The recovered concentrated magnetite is returned to sump 11through conduit 34.

The medium in sump 11 is circulated by pump 25 to coal-separating vessel12 through conduit 13.

In vibrator screen 16, clear water is brought in through conduit 35 andis sprayed through the sprayheads 36 onto the material on the portion ofvibrator screen deck 37 which is over rinsing sump 24. The water andother material forced thereby into sump 24 is transported throughconduit 38 by pump 41 and through sprayheads 26 onto screen deck 37 andinto sump 23. This arrangement is of advantage in that it cuts the waterrequired in half and yet gives a double rinsing action. In effect, itwashes the material in dirty water first (from sump 24 throughsprayheads 26) and then washes it off in clean water (from clear waterline 35 through sprayheads 36).

The water in rinsing sump 24 is somewhat dirty, since it has passedthrough the products on the portion of the screen deck 37 positionedover sump 24. However, the products on the screen deck 37 above sump 24have already been partly cleaned and so the water in sump 24 is not toodirty. This somewhat dirty water is passed through counterfiow pipeconduit 38 and sprayheads 26 to prerinse the products on screen deck 37above sump 23. By this arrangement, most of the separating mediumremaining on the coal and the refuse on the screen deck 37 above sump 24are washed off into sump 24 "and sprayed over the material on screen 37above washings sump 23. From sump 23 the magnetite and water aretransported by pump 27 through conduit 28 to magnetic separator 31 wherethe magnetite is recovered.

Recovery of the magnetite is so complete that the process uses only twobags (two hundred pounds) of magnetite in separating about four hundredfifty tons of raw coal a day.

Controlling the Density of the Medium In the constant recirculation ofthe separating medium through the system, its specific gravity variesbecause of the water enetering the system with the raw coal, and alsobecause of the small amount of magnetite which is lost by passing out ofthe system with the clean coal or with the refuse.

To compensate for the variation in the density of the separating medium,mounted on conduit 13 is a density measuring head 17 which includes aradioactive source and a radiation detector. The radio active sourcegenerates a. ray that is received by the radiation detector and isconverted into a signal proportional to the density of the separatingmedium. This signal is passed through electrical conductors 42 to apreamplifier 43, through electrical conductors 44 to a visual densityinstrument 45, and through electrical conductors 46 to a specificgravity recorder and controller 47.

In response to the signals from density measuring head 17, controller 47operates a magnetic feeder 48 (which adds magnetite to the system asdesired), and a motorized valve 51 (which adds water to the separatingmedium as desired).

Controller 47 is connected to magnetite feeder 48 through electricalconductors 52, proportioning relay 53, electrical conductor 54, Modutrolmotor 55, link 56, magnetite feeder control 57, and electricalconductors 59.

Controller 47 is connected to motorized valve 51 by electricalconductors 62.

A motorized by-pass valve 63 is also operated by controller 47, and itbleeds separating medium from conduit 13 through a conduit 64 tomagnetic separator 31. Controller 47 is connected to by-pass valve 63through conductors 52, proportioning relay 53, conductors 54, andconductors 65.

In normal operation, by-pass valve 63 is one-third open, and feeder 48is supplying magnetite to the system continuously at a rate whichcompensates for the small amount of magnetite which is being withdrawnfrom the system and lost with the cleaned coal and refuse.

If the density of the medium becomes too high, the high density issensed by density measuring head 17 and it transmits a signal tocontroller 47. Controller 47 shuts off magnetite feeder 48 to stop theadding of magnetite to the system, and opens water valve 51 to add waterto the system to bring the density of the separating medium back tonormal. Then, density measuring head 17 signals controller 47 to returnmagnetic feeder 48 to its normal position of adding magnetite to thesystem), and to close water valve 51.

If the density of the separating medium is too low, density measuringhead 17 signals controller 47 which operates feeder 48 to open it widerand thus add more magnetite. Controller 47 also opens by-pass valve 63wider (to its three-quarter open position) and bleeds more medium to themagnetic separator 31 where the water is removed and magnetite isrecovered. After the density returns to normal, density measuring head17 signals controller 47 to return feeder 48 and by-pass valve 63 tonormal position.

Magnetite is transferred from magnetite feeder 48 into the systemthrough conduit 66 which leads directly into main medium sump 11, but itwill be realized that the magnetite may be transferred into the systemat other points if desired.

In order to maintain a sufiicient amount of separating medium in thesystem, and also to prevent the medium from overflowing sump 11 whileits density is being adjusted, sump 11 is provided with level sensingand con trol means which includes a gamma ray source unit 67, high leveldetector 68, and low level detector 69.

Low level detector 69 is connected to a motorized valve 72 by electricalconductors 73, and when the level in the sump 11 becomes too low, asignal from detector 69 operates valve 72 to admit water from a watersource 74 through conduits 75, 76 into sump 11.

If the level of separating medium in sump 11 is too high, high leveldetector 68 sends a signal through electrical conductors 77 to closevalve 51 (overriding any signal from controller 47 which may have openedvalve 51 to lower the density of the medium) and stop any Water fromflowing through conduit 78 into sump 11.

a a a High level detector 68 also lowers the level of the medium in sump11 by sending a signal through electrical conductors 81 and 82 to openby-pass valve 63 wider (to its one-half open position) to bleed moremedium through conduit 64 to magnetic separator 31, and thereby removesome of the water from the system.

In normal operation with the level in sump 11 within the normal range,by-pass valve 63 is one-third open, and feeder 48 is feeding magnetitecontinuously to the system at a normal rate to maintain the density ofthe separating medium at a predetermined optimum. But if no raw coal isbeing fed into the system, no dilution of the medium occurs from wateron raw coal, and therefore the densifying operations of bleeding aportion of the medium to the magnetic separator and there dewatering itbefore returning it to the system, and of adding magnetite frommagnetite feeder 48 to the system, would make the medium too dense. Toavoid this, there is provided a recording ammeter 83 which is connectedto drive motor 84 by electrical conductors 85. Ammeter 83 measures thecurrent drawn by motor 84 and when the current drops below apredetermined value (which indicates that there is no load on feedconveyor 14), it sends a signal through conductors 86 and 58 to shut otfmagnetite feeder 48- and prevent it from adding magnetite to the system.Ammeter 83 also sends a signal through conductors 8 6, magnetite feedercontrol 57, link 56, Modutrol motor 55, and conductors 65, to shut offby-pass valve 63.

When raw coal is again being fed to the system, recording ammeter 83signals magnetite feeder 48 and bypass valve 63to return them to normalposition.

Density measuring head 17 directs rays from a shielded radioactivesource through conduit 13 and the separating medium, and measuresvariations in density as small as .001 specific gravity. A suitablemeasuring head 17 is manufactured by Industrial Nucleonics Corporation,Colurnbus, Ohio, and is known as Accu Ray Model PDH2.

The signal from measuring head 17 is amplified by preamplifier 43 andtransmitted through the visual density measuring instrument 45 tospecific gravity recorder and controller 47.

The specific gravity recorder and controller 47 may be the ElectronikCircular Chart Electric Controller Class '14 Special Line (S 142-1), andposition-controller (S 801-1 manufactured by Minneapolis-Honeywell Regulator Co. Controller 47 is an electric position-proportional controlwith automatic reset.

Proportioning relay 53 may be 9. R933 proportioning relay made byMinneapolis-Honeywell Regulator Co. and designed to controlproportioning motors of the industrial type.

Coal-separator vessel 12 may be a Wilmot OCC H.M. vessel as described inUS. Patent No. 2,752,040 and manufactured by Wilmot Engineering Company,White Haven, Pennsylvania.

Referring to FIG. 3 for afurther explanation of the motorized valveapparatus, the signal from density measuring head 17 is transmitted tocontroller 47 by electrical conductors 46. Controller 47 transmits asignal over conductors 62 to control unit 91 of motorized valve 51.Within control unit 91, the error signal from controller 47 is receivedby bridge 92 and is transmitted over conductors 95 to a servo amplifier93 which sends a signal over conductors 96 to actuate motor 98 to turnshaft 94 which is connected to the valve element in the conduit 78 (FIG.1).

Motor 98 (FIG. 3) is connected by electrical conductors 97 to bridge 92to provide a negative feedback which gives a subtractive signal tobridge 92 when the valve 51 is turned to the desired position so thatthe valve element avoids overshooting or hunting. The other motorizedvalves 63, 72 are similarly constructed.

' Excellent results have been obtained from the process and system ofthis invention. For example during one nine and one-half hour run of thesystem in actual 0peration, the specific gravity was continuouslyrecorded and the average variation in specific gravity from the 1.70optimum desired was only plus or minus 0.004 throughout the entireoperating period. This, of course, assures complete recovery of useablecoal and an absolutely uniform product no matter what the composition ofthe raw coal entering the breaker.

It is to be understood that the form of the invention herewith shown anddescribed is to be taken as a preferred embodiment. Various changes maybe made in the shape, size and arrangement of parts. For example,equivalent elements may be substituted for those illustrated anddescribed, parts may be reversed, and certain features of the inventionmay be utilized independently of the use of other features, all withoutdeparting from the spirit or scope of the invention as defined in thesubjoined claims.

The claimed invention:

1. A process of separating coal from raw coal containing coal and waste,comprising feeding water and finely divided magnetite to a mixing zoneto form a coalseparating slurry medium, feeding separating medium fromsaid mixing zone into a coal-separating zone, feeding raw coal to saidcoal-separating zone and there separating the coal from the waste bycausing the coal to float in the separating medium and the waste to sinktherein, separating a fraction of the medium from the coal and waste bydraining and returning it to said mixing zone, separating anotherfraction of the medium from the coal and Waste by diluting it,recovering magnetite from said dilute fraction and returning therecovered magnetite to said mixing zone, continuously measuring thedensity of the medium being fed to said coal-separating zone, andcontrolling said density by adding and subtracting water and magnetiteautomatically in response to said measuring.

2. A process of separating coal from raw coal containing coal and waste,comprising feeding water and finely divided magnetite to a mixing zoneto form a coal-separating slurry medium, feeding a portion of saidmedium from said mixing zone to a coal-separating zone, feeding raw coalto said coal-separating zone and there separating the coal from thewaste by causing the coal to float in said medium and the waste to sinktherein, separating magnetite from the coal and waste and returning itto said mixing zone, feeding another portion of said medium from saidmixing zone to a magnetite recovery zone and there separating out themagnetite, feeding the recovered magnetite to said mixing zone to makesaid medium more dense, continuously measuring the density of saidmedium being fed to said coal-separating zone, and controlling saiddensity by adding and subtracting Water and magnetite automatically inresponse to said measuring. 1

3. A process of separating coal from :raw coal containing coal andwaste, comprising feeding water and finely divided magnetite to a mixingzone to form a coalseparating slurry medium, feeding a portion of saidmedium from said mixing zone to a coal-separating zone, feeding raw coalto said coal-separating zone and there separating the coal from thewaste by causing the coal to float in said medium and the waste to'sinktherein, separating magnetite from the coal and waste and returning itto said mixing zone, feeding another portion of medium from said mixingzone to a magnetite recovery zone and there separating out magnetite,feeding the recovered magnetite from the magnetite recovery zone to saidmixing zone to make the medium more dense, automatically shutting oflsaid feeding of the medium to said magnetite recovery zone when no rawcoal is being fed to said coal-separating zone, automatically shuttingoff the feeding of water and magnetite to the medium in said mixing zonewhen no raw coal is being fed to said coalseparating zone, continuouslymeasuring the density of the medium being fed to said coal-separatingzone, and

7 controlling said density by adding and subtracting water and magnetiteautomatically in response to said measurmg.

4. A process of separating coal from raw coal containing coal and waste,comprising feeding water and finely divided magnetite to a mixing zoneto form a coal-separating slurry medium, automatically maintaining thelevel of the medium in the mixing zone, feeding a portion of the mediumfrom said mixing zone to a coal-separating zone, feeding raw coal tosaid coal-separating zone and there separating the coal from the wasteby causing the coal to float in medium and the waste to sink therein,separating magnetite from the coal and waste and returning it to saidmixing zone, feeding another portion of the medium from said mixing zoneto a magnetite recovery zone and there separating out magnetite, feedingthe recovered magnetite from said magnetite recovery zone to said mixingzone to make the medium more dense, automatically shutting off saidfeeding of a portion of the medium to said magnetite recovery zone whenno raw coal is being fed to said coal-separating zone, automaticallyshutting off the feeding of water and magnetite to the medium in saidmixing zone when no raw coal is being fed to said coal-separating zone,continuously measuring the density of the medium being fed to saidcoal-separating zone, and controlling said density by adding andsubtracting water and magnetite automatically in response to saidmeasuring.

5. A process of separating an ore from raw ore containing ore and waste,comprising feeding a liquid and a finely divided insoluble material to amixing zone to form an ore-separating slurry medium, feeding medium fromsaid mixing zone to an ore-separating zone, feeding raw ore to saidore-separating zone and there separating the ore from the waste,separating said finely divided material from the ore and waste andreturning it to said mixing zone, continuously measuring the density ofthe medium being fed to said ore-separating zone, and controlling saiddensity by adding and subtracting liquid and finely divided insolublematerial automatically in response to said measuring.

6. A process of separating an ore from raw ore containing ore and waste,comprising feeding a liquid and a finely divided insoluble material to amixing zone to form an ore-separating slurry medium, automaticallymaintaining the level of the medium in the mixing zone, feeding mediumfrom said mixing zone to an ore-separating zone, feeding raw ore to saidore-separating zone and there separating the ore from the waste,separating finely divided material from the ore and waste and returningit to said mixing zone, continuously measuring the density of the mediumbeing fed to said ore-separating zone, and controlling said density byadding and subtracting liquid and finely divided insoluble materialautomatically in response to said measuring.

7. A process of separating an ore from raw ore containing ore and waste,comprising feeding a liquid and a finely divided insoluble material to amixing zone to form an ore-separating slurry medium, feeding a portionof the medium from said mixing zone to an ore-separating zone, feedingraw ore to said ore-separating zone and there separating the ore fromthe waste, separating said finely divided material from the ore andwaste and returning it to said mixing zone, feeding another portion ofthe medium from said mixing zone to a recovery zone and there separatingout finely divided material, feeding the recovered finely dividedmaterial from said recovery zone to said mixing zone, continuouslymeasuring the density of the medium being fed to said ore-separatingzone, and controlling said density by adding and subtracting liquid andfinely divided insoluble material automatically in response to saidmeasuring.

8. A process of separating an ore from raw ore containing ore and waste,comprising feeding a liquid and a finely divided insoluble material to amixing zone to form an ore-separating slurry medium, feeding a portionof medium from said mixing zone to an ore-separating zone, feeding rawore to said ore-separating zone and there separating the ore from thewaste, separating finely divided material from the ore and waste andreturning it to said mixing zone, feeding another portion of medium fromsaid mixing zone to a recovery zone and there separating out finelydivided material, feeding the recovered finely divided material fromsaid recovery zone to said mixing zone, automatically shutting off saidfeeding of a portion of the medium to said recovery zone when no raw oreis being fed to said ore-separating zone, automatically shutting off thefeeding of water and magnetite to the medium in said mixing zone when noraw ore is being fed to said ore-separating zone, continuously measuringthe density of the medium being fed to said ore-separating zone, andcontrolling said density by adding and subtracting liquid and finelydivided insoluble material automatically in response to said measuring.

9. A process of separating an ore from raw ore containing ore and waste,comprising feeding a liquid and a finely divided insoluble material to amixing zone to form an ore-separating slurry medium, automaticallymaintaining the level of the medium in the mixing zone, feeding aportion of said medium from said mixing zone to an ore-separating zone,feeding raw ore to said oreseparating zone and there separating the orefrom the waste, separating finely divided material from the ore andwaste and returning it to said mixing zone, feeding another portion ofsaid medium from said mixing zone to a recovery zone and thereseparating out finely divided material, feeding said recovered finelydivided material to said mixing zone, automatically shutting off saidfeeding of a portion of said medium to said recovery zone when no rawore is being fed to said ore-separating zone, automatically shutting offthe feeding of water and magnetite to the medium in said mixing zonewhen no raw ore is being fed to said ore-separating zone, continuouslymeasuring the density of said medium being fed to said oreseparatingzone, and controlling said density by adding and subtracting said liquidand said finely divided mate rial automatically in response to saidmeasuring.

10. A system for separating coal from raw coal containing coal andwaste, comprising a mixing sump into which is fed water and finelydivided magnetite to form a coal-separating slurry medium, acoal-separating vessel which receives the medium through a conduitextending from said sump and in which the coal separates from the wasteby floating in the medium, means for feeding raw coal into saidcoal-separating vessel, means connected into said system for separatinga fraction of the medium from the coal and waste and returning it tosaid sump, means for separating another fraction of the medium from thecoal and waste by diluting it, means for recovering magnetite from saiddilute fraction and returning the recovered magnetite to said mixingsump, and density sensing and control means connected in said system forcontinuously measuring the density of the medium being fed to saidcoal-separating vessel and automatically controlling said density byadding and subtracting water and magnetite to and from said system inresponse to said measuring.

11. A process of separating coal from raw coal con taining coal andwaste, comprising feeding water and finely divided magnetite to a mixingzone to form a coalseparating slurry medium, feeding separating mediumfrom said mixing zone into a coal-separating zone, feeding raw coal tosaid coal-separating zone and there separating the coal from the wasteby causing the coal to float in the separating medium and the waste tosink therein, separating magnetite from the coal and waste, returningsaid separated magnetite to the mixing zone, continuously measuring thedensity of the medium being fed to said coal-separating zone, andcontrolling said 9 density by adding and subtracting water and magnetiteautomatically in response to said measuring.

12. A system for separating coal from raw coal containing coal andwaste, comprising a mixing sump into which is fed water and finelydivided magnetite to form a coal-separating slurry medium, acoal-separating vessel to which said medium is fed from said sump and inwhich the coal is separated from the waste by floating in the medium,means for feeding raw coal into said coalseparating vessel, meansconnected into said system for separating magnetite from the coal andwaste, means for returning said separated magnetite to the mixing sump,and density sensing and control means connected in said system forcontinuously measuring the density of the medium being fed to saidcoal-separating vessel and automatically controlling said density byadding and subtracting water and magnetite to and from said system inresponse to said measuring.

13. The system defined in claim 12, wherein said density sensing andcontrol means includes a density measuring instrument having aradioactive source and a radiation detector which generates a signalproportional to the density of the medium, a magnetite feeder connectedto said system, a water source connected to said system by a motorizedvalve, and means connected to said density measuring instrument andresponsive to said signal for operating said magnetite feeder and saidmotorized valve to add magnetite and water as necessary to maintain thedesired density of the medium.

14. A system for separating coal from raw coal containing coal andwaste, comprising a mixing sump into which is fed water and finelydivided magnetite to form a coal-separating slurry medium, acoal-separating vessel which receives the medium through a conduitextending from said sump and in which the coal separates from the wasteby floating in the medium, means for feeding raw coal into saidcoal-separating vessel, mean-s connected into said system for separatingmagnetite from the coal and waste, means for returning said separatedmagnetite to said sump, magnetite-separating means for separating outmagnetite, bleed means for feeding a portion of the medium from saidsump to said magnetiteseparating means, means for feeding the recoveredmagnetite from said magnetite-separating means to said mixing sump tomalee the medium therein more dense, and density sensing and controlmeans connected in said system for continuously measuring the density ofthe medium being fed to said coal-separating vessel and automarticailycontrolling said density by adding and subtracting water and magnetiteto and from said system in response to said measuring.

15. A system for separating coal irom raw coal con taining coal andWaste, comprising a mixing sump into which is fed water and finelydivided magnetite to form a coal-separating slurry medium, acoal-separatnig vessel which receives the medium through a conduitextending from said sump and in which the coal separates from the wasteby floating in the medium, means for feeding raw coal into saidcoal-separating vessel, means connected into said system for separatingmagnetite from the coal and waste, means for returning said separatedmagnetite to said sump, magnetite-separating means for separating outmagnetite, bleed means for feeding a portion of the medium from saidsump to said magnetite-separating means, means for feeding the recoveredmagnetite from said magnetite-separating means to said mixing sump tomake the medium therein more dense, means connected to said raw coalfeed means and operative in response thereto for automatically shuttingoff said bleed means when no raw coal is being fed to saidooal-separating vessel, and density sensing and control means connectedin said system for continuously measuring the densify of the mediumbeing fed to said coal-separating vessel and automatically controllingsaid density by adding and 10 subtracting water and magnetite to andfrom said system in response to said measuring.

16. The system defined in claim 15, wherein said means for automaticallyshutting off said bleed means oomprises an arnmeter connected to saidraw coal feed means, said ammeter generating a signal responsive to thecurrent in said conveyor motor, and a motorized valve posi- Itioned in abypass pipe of said bleed means and electrically connected to saidammeter and adapted to shut off said by-pass pipe in response to saidsignal.

17. A system for separating one from raw ore containing ore and waste,comprising a mixing sump into which is fed a liquid and a finely dividedinsoluble material to form an oreseparating slurry medium, anorcseparating vessel which receives the medium through a conduitextending from said sump and in which the ore separates from the wasteby floating in the medium, means for feeding raw ore into saidore-separating vessel, means connected into said system for separatingfinely divided material from the ore and waste, means for returning saidseparated material to said sump, and density sensing and control meansconnected in said system for continuously measuring the density of themedium being fed to said ore-separating vessel and automaticallyeonttrolling said density by adding and subtracting the liquid andfinely divided insoluble material to and from said system in response tosaid measuring.

18. The system defined in claim 17, wherein said density sensing andcontrol means includes a density measuring instrument having aradioactive source and an nadiation detector which generates a signalproportional to the density of the medium, a feeder for said insolublematerial connected to said system, a water source connected to saidsystem by a motorized valve, and means responsive to said signal foropenaiting said feeder and said motorized valve to add the finelydivided insoluble material and the liquid as necessary to maintain thedensity of the medium.

19. A system for separating ore from raw ore containing ore and waste,comprising a mixing sump into which is fed a liquid and a finely dividedinsoluble material to form an ore-separating slurry medium, anore-separating vessel which receives said medium through a conduitextending from said sump and in which the ore separates from the Wasteby floating in the medium, means for feeding raw ore into saidore-separating vessel, means connected into said system for separatingfinely divided material from the ore and waste, means for returning saidseparated material to said sump, means for separating out finely dividedinsoluble material, bleed means for feeding a portion of the medium fromsaid sump to said insoluble material separating means, means for feedingthe recovered insoluble material from said material separating means tosaid mixing sump to make the medium therein more dense, and densitysensing and control means connected in said system for continuouslymeasuring the density of the medium being fed to said ore-separatingvessel and automatically controlling said density by adding andsubtracting liquid and finely divided insoluble material to and fromsaid system in response to said measuring.

20. A system for separating ore from raw ore containing ore and waste,comprising a mixing sump into which is fed a liquid and a finely dividedinsoluble material to form an ore-separating slurry medium, anore-separating vessel which receives the medium through a conduitextending from said sump and in which the ore separates from the wasteby floating in the medium, means for feeding raw ore into saidore-separating vessel, means connected into said system for separatingfinely divided material from the ore and waste, means for returning saidseparated material to said sump, means for separating out insolublematerial, bleed means for feeding a portion of the medium from said sumpto said insoluble material separating means, means for feeding therecovered insoluble material from said material separating means to saidmixing zone to make the medium therein more dense, means connected tosaid raw or feed means and operative in response thereto forautomatically shutting off said bleed means when no raw ore is being 5fed to said ore-separating vessel, means connected to said raw ore feedmeans and operative in response thereto for automatically shutting offfeeding of said insoluble material into the medium in said mixing sump,and density sensing and control means connected in said system 10 31 57for continuously measuring the density of the medium being fed to saidore-separating vessel and automatically controlling said density byadding and subtracting liquid and finely divided insoluble material toand from said system in response to said measuring.

21. The system defined in claim 20, wherein said means for automaticallyshutting off said bleed means comprises an ammeter connected to said rawore feed means, said ammeter generating a signal responsive to thecurrent in said conveyor motor, and a motorized valve positioned in abypass pipe of said bleed means and electrically connected to saidammeter and adapted to shut off said by-pass pipe in response to saidsignal.

References Cited in the file of this patent UNITED STATES PATENTS

1. A PROCESS OF SEPARATING COAL FROM RAW COAL CONTAINING COAL AND WASTE,COMPRISING FEEDING WATER AND FINELY DIVIDED MAGNETITE TO A MIXING ZONETO FORM A COALSEPARATING SLURRY MEDIUM, FEEDING SEPARATING MEDIUM FROMSAID MIXING ZONE INTO A COAL-SEPARATING ZONE, FEEDING RAW COAL TO SAIDCOAL-SEPARATIG ZONE AND THERE SEPARATING THE COAL FROM THE WASTE BYCAUSING THE COAL TO FLOAT IN THE SEPARATING MEDIUM AND THE WASTE TO SINKTHEREIN, SEPARATING A FRACTION OF THE MEDIUM FROM THE COAL AND WASTE BYDRAINING AND RETURNING IT TO SAID MIXING ZONE, SEPARATING ANOTHERFRACTION OF THE MEDIUM FROM ARATING THE COAL FROM THE WASTE BY CAUSINGTHE COAL TO FROM SAID DILUTE FRACTION AND RETURING THE RECOVEREDMAGNETITE TO SAID MIXING ZONE, CONTINUOUSLY MEASURING THE DENSITY OF THEMEDIUM BEING FED TO SAID COAL-SEPARATING ZONE, AND CONTROLLING SAIDDENSITY BY ADDING AND SUBTRACTING WATER AND MAGNETITE AUTOMATICALLY INRESPONSE TO SAID MEASURING.